Cluster headache and oxygen: is it possible to predict which patients will be relieved? A prospective cross-sectional correlation study.

Response to 100 % oxygen as acute treatment for cluster headache is relative low considering certain subgroups or predictors. The primary purpose of the present study was to find prospectively which factors differ between responders and non-responders to oxygen therapy. The second goal was to find whether any of these differences would clarify the mechanism of pain reduction by oxygen and cluster headache pathophysiology. Patients diagnosed with cluster headache according to the ICHD-II criteria, who started on oxygen therapy (n = 193), were recruited from 51 outpatient clinics and via patient websites in The Netherlands. Patients had to return two questionnaires around the start of oxygen therapy (n = 120). Eventually, 94 patients were included. Clear non- plus moderate responders had ever used pizotifen more often (p = 0.03). Clear non-responders more often had photophobia or phonophobia during cluster headache attacks (p = 0.047) and more often had used triptans in the same active phase as the phase in which they had used oxygen for the first time (p = 0.02). Using correction for multiple testing, we could only confirm a statistically significant difference in triptan use. We were unable to locate the level of action of oxygen in the thalamus and cortex or confirm the sites of its action presently known, solely based on current knowledge of photophobia circuits. However, we conclude that particularly the higher frequency of photophobia or phonophobia in clear non-responders deserves further study to understand the mechanism of pain reduction by oxygen and cluster headache pathophysiology.